The utility of measuring blood flow velocity, e.g., at a region proximate a tricuspid valve of a heart, such as for the purpose of cardiac pacing and control has been described in the art. For example, U.S. Pat. No. 5,243,976 to Ferek-Petric entitled “Tricuspid Flow Synchronized Cardiac Electrotherapy System with Blood Flow Measurement Transducer and Controlled Pacing Signals Based on Blood Flow Measurement,” issued Sep. 14, 1993, and U.S. Pat. No. 5,316,001 to Ferek-Petric et al. entitled “Cardiac Measurement System for Measuring Blood Flow Velocity by Use of a Sensor Implanted Inside the Heart,” issued May 31, 1994, disclose the utility of pulsed wave and continuous wave Doppler methods for blood flow velocity measurement within the tricuspid valve. An implantable lead design was also described that emphasized a Doppler sensitive volume of blood flow. Further, U.S. Pat. No. 5,318,595 to Ferek-Petric et al. entitled “Pacing Method and System for Blood Flow Velocity Measurement and Regulation of Heart Stimulating Signals Based on Blood Flow Velocity,” issued Jun. 7, 1994, discloses a method of the closed loop A-V interval regulation.
Although continuous wave Doppler methods provide continuous monitoring of blood flow velocity, the method may undesirably deplete the stored energy of IMD power sources. Further, continuous wave Doppler methods may not have the depth resolution and range accuracy of pulsed wave Doppler methods.
Pulsed Doppler ultrasound is an accurate method of measuring blood flow velocity. However, pulsed Doppler ultrasound is not very convenient for implantable medical devices (IMDs) because of the limited energy storage available in today's power sources.
Table 1 below lists U.S. patents relating to various ultrasound techniques.
TABLE 1Patent No.InventorIssue Date5,183,040Nappholz et al.Feb. 2, 19935,243,976Ferek-Petric et al.Sep. 14, 19935,316,001Ferek-Petric et al.May 31, 19945,318,595Ferek-Petric et al.Jun. 7, 1994
All documents listed in Table 1 above and further elsewhere herein are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Embodiments, and claims set forth below, many of the devices and methods disclosed in the documents of Table 1 and other documents incorporated by reference herein may be modified advantageously by using the teachings of the present invention.